The Indus Dictionary Project
This is a pictograph of a siphon. The pictograph gives us the first meaning for this symbol, which is the adjective racked.
The symbol was also used in a more general sense to refer to pipes. Therefore, the second definition is the noun pipe.
Harappa: Pottery: H-1092 A: Asko Parpola, B. M. Pande, and Petteri Koskikallio, 2010: Corpus of Indus Seals and Inscriptions: Volume 3,1: Page 152: New material, untraced objects, and collections outside India and Pakistan: Suomalainen Tiedeakatemia.
Example H-1092 consists of a single character stamped near the rim of a pottery jar. The jar would probably have contained alcohol made from barley. The siphon symbol indicates that the alcohol had been racked; that is separated from the sediment by means of siphoning.
Indus Script Sign Number 1004 (a pipe): List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.